Physics conceptual questions 1-9
What is the minimum amount of work required to raise a 20 kg mass 3 meters vertically upward?
590 J
The speed of light is 3 ✕ 108 m/s. How many kilometers does light travel in one second?
3 ✕ 10^5
Bekki walks 3 m to the right, 4 m to the left, 5 m to the right, and 2 m to the left. What is her displacement?
2 m (to the right)
What did the speed vs. time graph for the wood block indicate about its acceleration?
The acceleration was constant but not zero.
Two equal-mass balls swing down and hit identical bricks while traveling at identical speeds. Ball A bounces back, but ball B just stops when it hits the brick. Which ball has a better chance of knocking the brick over?
A
A block having mass m travels along a horizontal frictionless surface with speed v. What is the LEAST amount of work that must be done on the mass to reverse its direction?
0
Two blocks, M2 > M1, having the same kinetic energy move from a frictionless surface onto a surface having friction coefficient μk.
M1
You throw a ball vertically upward. Which statement best describes the direction and magnitude of the ball's acceleration while the ball is still moving up?
downward, constant magnitude
A polar bear is sitting on a sheet of ice that is being carried by the current away from the north pole at a speed of 1 m/s. A fish is swimming toward the north pole at a speed of 10 m/s relative to the current. What is the speed of the fish with respect to the bear?
10 m/s
A student suggests that an unknown mass can be measured by placing a known mass on a frictionless incline and measuring the acceleration. Then place the unknown mass on the same incline and measure the acceleration. From this information you can find the value of the new mass. Will this work? Be prepared to explain.
No
Two balls, one twice as massive as the other, are dropped from the roof of a building (freefall). Just before hitting the ground, the more massive ball has ______ the kinetic energy of the less massive ball. (Neglect air friction.)
Twice
A 75 g metal sphere is attached to one end of a light thin rod, and a 25 g sphere is attached to the other end, with a distance d between the centers of the two spheres, as shown in the figure below.
a distance 1/4d from the center of the 75 g sphere
You throw a ball vertically upward. Which statement best describes the direction and magnitude of the ball's velocity while the ball is still moving up?
upward, decreasing magnitude
The graph shows the magnitude of the spring force versus displacement plots for three springs. Rank in order, from largest to smallest, the spring constants k1, k2, and k3.
k1 > k2 > k3
In the video vignette, you created a velocity vs. time graph for a moving rocket cart on a tennis court. Which of the following best describes the shape of the velocity vs. time graph you produced for the rocket cart?
a straight line with a nonzero, positive slope
In the video, you clicked on the center of the moving wooden block to create a plot of its speed vs. time. Which of the following best describes the shape of the resulting speed vs. time graph?
a straight line with a noticeably negative slope
A cart with mass m2 is connected to a mass m1 using a string that passes over a frictionless pulley, as shown below. Initially, the cart is held motionless. After the cart is released, the tension in the string
decreases
Consider the arrangement of pulleys and masses shown below. The masses of the pulleys are small. Ignore friction. For what relationship of the masses would the masses remain at rest?
m/M = 0.5
The plot of position versus time is shown for three objects. Which object has the largest acceleration at t = 2.5 s?
object A only (curving upward)
A sports car accelerates from zero to 30 mph in 1.5 s. How long would it take to accelerate from zero to 60 mph, assuming the power of the engine to be independent of velocity and neglecting air drag?
6 s
A cat spots a flowerpot that sails up past an open window. The pot, which passed by very close to the window, is in view for 0.25 s while going up, and the top-to-bottom height of the window is 2.00 m. Intermediate step: What is the pot's upward velocity at the bottom of the window?
9.23 m/s
You throw a ball vertically upward. The ball moves up, reaches its highest point, and finally falls down. Which of the following graphs best represent the ball's acceleration and velocity vs. time during the process?
Straight line in negative Y value
Two blocks with mass m2 > m1 sit on a horizontal surface having friction. Both blocks are pulled with a constant speed, but v2 < v1, by a rope under tension. (Assume the coefficient of kinetic friction is the same for both blocks.)
T2 because mass is bigger
The collision between the lighter and heavier carts is shown again with a small toy figure riding on each cart. Which of the following statements is true about the different effects on the toy figures during the collision?
The force each cart exerts on the other has the same magnitude. However, the lighter cart has a lower mass than the heavier cart, and therefore, according to Newton's second law, it has a greater acceleration than the heavier cart.
Later in the vignette, a video of a collision between a cart with a large mass and one with a small mass is shown. Again, the forces during the collision are plotted. What does the plot of the forces indicate in this case?
The forces that the carts exert on each other during the collision have the same magnitude but opposite directions.
A block having mass m moves along an incline having friction as shown in the diagram above. The spring is extended from its relaxed length. As the block moves a small distance up the incline, how many forces do work on the block?
four forces
One cue ball hits an object ball. The cue ball's motion is at a 90° angle to the motion of the object ball after the collision. The ratio of speed of the cue ball after the collision and the object ball is 1 : sqrt(3). What is the ratio of the initial and final speed of the cue ball? All balls have the same mass.
2 : 1
A car travels directly north on a straight highway at a constant speed of 80 km/hr for a distance of 25 km. The car then continues directly north at a constant speed of 50 km/hr for a distance of 75 more kilometers. The average speed of the car for the entire journey is closest to
55.2 km/hr
In a physics lab, a pendulum hung from the ceiling slowly swings back and forth. Select the arrow pointing closest to the direction of its acceleration when it is at its lowest at point C.
Arrow going up
A block moves with a constant velocity to the right on a surface that has friction. Which of the following most closely resembles the correct freebody diagram for all forces acting on the block?
Forces going up, down, left, and right
A car rounds a circle while maintaining a constant speed. Which arrow represents the direction of the net force on the car as it rounds the curve at the instant shown below?
Going towards middle of circle
Based on your measurements, which of the following statements are true about the ball's velocity? I: The horizontal component of the ball's velocity is constant. II: The vertical component of the ball's velocity is constant.
Statement I is true.
Based on your measurements, which of the following statements are true about the distance the ball travels in successive equal time intervals? I: The horizontal distance the ball moves in successive equal time interval stays the same. II: The vertical distance the ball moves in successive equal time intervals stays the same.
Statement I is true.
Which of the following best explains why the dancer in the video appears to "float" in midair for a few tenths of a second during her leap?
The dancer moves her legs and arms upward during the leap. This shifts her center of mass upward. Because of this, her head appears to "float", but her center of mass actually rises and falls in parabolic motion, like a point object.
Using Newton's second law and the velocity vs. time graph for the rocket cart, what can you conclude about the net force on the rocket cart from the time when it was first released to just before it was caught by the rope?
The net force on the cart was approximately constant but not zero.
Based on Newton's first law, what can you say about the motion of the dry ice puck and the net force on it?
The net force on the dry ice puck was essentially zero. This is why it continued in a straight line at a constant speed until it was caught.
The object in the figure below consists of three spheres, each connected to the other by springs, and each with a different mass. The object is tossed into the air, and it tumbles, vibrates, and spins as it moves through the air. Ignoring air resistance, which of the following best describes the motion of the object in the air?
The path that the center of mass of the entire object takes will be a parabola.
Consider two objects, where the second object is twice as massive as the first. The same net force acts on each object. Based on Newton's second law, which of the following is true about the acceleration of the two objects?
The second, more massive object will have half the acceleration as the first object.
Based on Newton's first law, what can you say about the motion of the wood block and the net force on it?
There was a net force on the wood block which caused it to slow down and stop.
In science, "light year" is used to measure how far light travels in a year. According to this definition, which of the following units is correct for "light year"?
m (meter)
A 20 gram bullet with an initial velocity v is shot into a 5 kg wood block attached to the ceiling with massless strings. While the block with the bullet stuck inside is swinging upward, which of the following quantities is conserved?
sum of kinetic plus potential energy
A sports car accelerates from rest. Assume that the power of the engine is independent of velocity and neglect air drag, etc. Which of the following graphs best represents the speed of the car as a function of time?
Going up gradually leveling out
A ladybug sits at the outer edge of a merry-go-round, and a gentleman bug sits halfway between her and the axis of rotation. The merry-go-round makes a complete revolution once each second. (Assume non-zero frictional force and the same coefficients of friction for both bugs.) The gentleman bug's speed is
Half the ladybug's.
According to the definition of "light year" (the distance traveled by light in a year), we know: 1 light year =
3 X 108 ✕ 365 ✕ 24 ✕ 60 ✕ 60 m
In the video above, when you clicked on the center of the ball to track its horizontal (x-direction) motion, what did you notice about the separation between the vertical lines?
The separation between successive lines was about equal.
When you clicked on the center of the ball to track its vertical (y-direction) motion, what did you notice about the separation between the horizontal segments?
The separation between successive segments first decreased and then increased with time.
A car rounds a circle while maintaining a constant speed. At the instant shown below, is the car being accelerated as it rounds the curve?
Yes
Later in the video you created two velocity vs. time graphs for a fan cart moving on a track. In the first case, the cart had a small mass. For the velocity vs. time graph you created for the fan cart with the small mass, which of the following best describes the shape of the graph?
a straight line with a nonzero, positive slope
A student steps onto a bathroom scale in a stationary elevator on the first floor of the Acme Building. The elevator accelerates until it reaches the second floor and then continues at constant speed until the 5th floor, where it starts slowing and stops on the 6th floor. Which sketch of weight shown on the scale vs. time during the entire process is most likely to be correct?
upside down u, straight line, then u
Two vehicles of mass M and 2M are moving in the same direction on a highway. Both drivers apply their brakes at the same time and both vehicles begin sliding. If the coefficient of kinetic friction μk is the same for both vehicles, how do their accelerations a1 and a2 compare?
a1 is the same as a2.
A 2 kg particle has an initial velocity of (5 − 4) m/s. Sometime later, its velocity is (7 + 3) m/s. What is the net work done on the particle during this time interval?
17 J
A block of mass m is at rest at the top of a ramp of vertical height h. The block starts to slide down the frictionless ramp and reaches a speed v at the bottom. If the same block were to reach a speed 2v at the bottom, it would need to slide down a frictionless ramp of vertical height _____.
4h
A battleship simultaneously fires two identical shells with the same initial speed at enemy ships. If the shells follow the trajectories shown and hit the enemy ships at the same height above sea level, which shell has the larger kinetic energy just before it hits the enemy ship? (Ignore air resistance.)
Both have the same kinetic energy.
Two masses, M > m, travel down the surfaces shown. Both surfaces are frictionless. Which mass has the largest speed at the bottom?
Both have the same speed.
Now, the turntable stops rotating, and the ladybug and the gentleman bug move to opposite edges of the outer rim. The gentleman bug has not watched his weight and is much more massive. The turntable then begins rotating ever more rapidly. Who will fall off first? (Assume non-zero frictional force and the same coefficients of friction for both bugs.)
Both will fall off at about the same time.
A block moves with a constant velocity to the right on the frictionless surface. Which of the following most closely resembles the correct freebody diagram for all forces acting on the block?
Force going up and down
A block sits at rest and stays at rest on a slide with frictional surfaces. Which of the following sketches most closely resembles the correct freebody diagram for all forces acting on the block? Each red arrow represents a force. Observe their number and direction, but ignore their lengths.
Forces going up, directly down, and opposite way its sliding
A small ball is released from rest at position A and rolls down a vertical circular track under the influence of gravity. When the ball reaches position B, which of the indicated directions most nearly corresponds to the direction of the ball's acceleration?
Going towards the right
The video vignette you just watched showed the motion of an object that consisted of a large sphere attached by a lightweight spring to a small base. The spring was compressed and the entire object launched into the air. Based on the video analysis of the motion, which of the following statements best describe the motion of the object while it was in the air?
Only the entire object's center of mass experienced a constant acceleration.
A block attached to a spring is oscillating between point X (fully compressed) and point Y (fully stretched). At point X, which of the following quantities would reach its maximum value?
The spring's potential energy The magnitude of the block's acceleration
HOW MANY of the identified objects are NOT accelerating? a race car going around a circular track at 150 MPH a sky diver falling at a constant speed a heavy box sliding across the floor, after being released a bowling ball colliding with a pin a vibrating guitar string a baseball flying through the air a child swinging on a swing
one
A person throws a ball straight up in the air. The ball rises to a maximum height and then falls back down so that the person catches it. Consider the ball while it is in the air. Which of the following statements are true? Just after the ball leaves the person's hand the direction of the acceleration is up. The acceleration is zero when the ball reaches its maximum height. The acceleration is about 9.8 m/s2 (down) when the ball is falling.
only C
Suppose you are on a cart initially at rest that rides on a frictionless track. If you throw a ball off the cart towards the left, will the cart be put into motion?
Yes, and it moves to the right.
A car of mass M is moving on a highway. The driver applies the brakes and the car starts to slide. Assuming a coefficient of kinetic friction μk, what is the car's acceleration?
−μkg
A spring-loaded toy dart gun shoots a dart to a maximum height of 24 meters. The same dart is again shot upward, but this time the spring is compressed only half as far before firing. Neglecting friction and assuming an ideal spring, how far up does the dart go this time?
6 m
The second time you created a velocity vs. time graph, the fan cart had twice the mass as in the initial run. Which of the following is true about the acceleration of the fan cart which had double the mass?
The acceleration of the fan cart was approximately half as much as it was for the first run.
A ball is rolled off the edge of a 1 meter high table. It lands on the floor 1.5 meters away from the edge of the table. If another ball is thrown straight down from a height of 1.0 meter the instant the first ball rolls off the table, which ball will hit the floor first?
The ball that was thrown down will hit the floor first.
A 16-kg ball is released into a tank of liquid and its speed increases from zero to 3.0 m/s in 2 seconds. What is the net work done on the ball in this 2 second interval?
+72 J
Two identical balls with different initial speeds slide down two frictionless tracks of the same height but different angles, and then reach the bottom. Which of the following quantities is (are) equal for these two processes?
1. The work done by the earth 2. The change of the ball's kinetic energy
A 20 g bullet is shot with an initial velocity v into a 5 kg wood block attached to the ceiling with massless strings. The collision happens so rapidly that the block doesn't change position appreciably until after the bullet stops. When does the momentum of the bullet plus block remain constant?
1. When the bullet approaches. 2. When the bullet stops
A metal ball is dropped and hits the ground. When the ball has penetrated well into the ground but hasnÂt yet stopped, what is the relationship between the magnitudes of the force FBG exerted on the ball by the ground and the force FGB exerted on the ground by the ball?
FBG = FGB
Based on your measurements, which of the following statements are true about the ball's acceleration? I: The horizontal component of the ball's acceleration is zero. II: The vertical component of the ball's acceleration is zero.
Statement I is true.
What did your velocity vs. time graph for the dry ice puck indicate about its acceleration?
The acceleration was essentially zero.
Consider the collision between the carts of unequal masses shown in vignette. Which of the following statements is true about the forces exerted by the carts on each other during this collision?
The forces are equal in magnitude and opposite in direction according to Newton's third law.
The first collision shown in the video is one between two identical carts moving at the same speed. The forces that each cart exerts on the other during the collision is plotted. What does the plot of the forces indicate?
The forces that the carts exert on each other during the collision have the same magnitude but opposite directions.
A person sits in an office chair with small wheels that swivel. The person claims she can move the chair across the room without touching anything but the chair, simply by kicking her legs outward. Which of the following is true?
This claim is consistent with Newton's laws and can be done.
A car starting from rest speeds up to 30 m/s with a constant acceleration over a time of 10 seconds. Then, it travels at 30 m/s for 10 seconds, and finally brakes to a stop in 20 seconds with a constant deceleration. Which of the following graphs represents its graph of speed versus time?
Trapezoid Shape Graph
A constant force is exerted on a cart that is initially at rest on a frictionless air track. The force acts for a short time interval and gives the cart a final speed. To reach the same speed using a force that is half as big, the force must be exerted for a time interval that is
Twice as long
A satellite travels with a constant speed |v| as it moves around a circle centered on the earth. How much work is done by the gravitational force F on the satellite after it travels half way around the earth in time t?
W = F|v|t
A car traveling to the right with a speed v brakes to a stop in a distance d. The work done on the car by the frictional force F is: (Assume that the frictional force is constant.)
W = −Fd
A block of mass m sits at rest on a rough incline of angle 𝜃. The coefficient of static friction is μ.
mg sin(𝜃), up the incline.
A soccer ball rolls slowly across the road and down a hill as shown below: Which of the following sketches of ax vs. t is a reasonable representation of the horizontal acceleration of the ball as a function of time?
none of the above
In a physics lab, you place a block on the top of a low-friction ramp. The block slides down the ramp, around a circular part at the bottom, up a ramp on the other side, and then shoots off the end. Is the net force on the block zero at any of the points A, B, C or D?
none of the above
A soccer ball rolls across the road and down a hill as shown below. Which of the following sketches of Fy vs. t represents the net vertical force on the ball as a function of time? (Assume up is the +y-direction.)
on the x axis then below x axis
A car makes a left hand turn at a constant speed in a time interval Δt. Initially its velocity is north and after turning its velocity is west. What direction does the average acceleration vector for this car in the time Δt point?
southwest
A cat spots a flowerpot that sails up past an open window. The tiny pot, which passed by very close to the window, is in view for 0.25 s while going up, and the top-to-bottom height of the window is 2.00 m. How high above the top of the window does the flowerpot go? Can you solve this question in one step using one of the constant acceleration equations below? v = v0 + at x − x0 = v0t + 1/2at^2 v^2 = v0^2 + 2a(x − x0) x − x0 = 1/2(v0 + v)t x − x0 = vt − 1/2at^2
No - Since one must first calculate the velocity and then calculate the maximum height, the answer cannot be derived by plugging into a single equation.
Which of the following best describes the shape of the graph of speed vs. time you found for the dry ice puck?
a straight line with essentially zero slope
A large skinny guy with mass 2M and a smaller guy with mass M are holding onto a massless pole while standing on frictionless ice, as shown below. If the little guy pulls himself toward the big guy, where would they meet?
−1 m
Two blocks, M = 2m, sit on a horizontal frictionless surface with a compressed massless spring between them. After the spring is released M has velocity v. The total energy initially stored in the spring was which of the following?
3mv2
A small guy moving at a high speed collides with a stationary large football player. Which person experiences the larger average force during the collision?
Both experience the same force.